The shy, white-bearded monkeys depend on wet environments and, like most primates, have rarely been known to travel more than a few kilometers from their normal range.

So when Iregi Mwenja, a researcher with Kenya's Institute for Primate Research, looked into reports that the monkeys were living in Mathews Range—a tiny pocket of lush forest some 90 miles (150 kilometers) from the closest known De Brazza's habitat—some experts were perplexed.

"When I told people that there were De Brazza's in Mathews, they said that that was not true," Mwenja said.

"I was almost doubting if it was true myself, but I had to go. The first thing is that I was shocked, because I had never seen such a large number of groups in such a small area before."

Monkeys "Just Hanging On"

Based on his survey, Mwenja puts the total number of De Brazza's living at Mathews Range between 200 and 300, bringing the total number of the monkeys in Kenya to 1,000.

Though there are about a hundred thousand De Brazza's living in the dense, little-developed forests of central and western Africa, populations of the monkeys in Kenya, Uganda, and Ethiopia exist only in small pockets that are isolated from the larger groups (see map of Africa).